1. Field of the Invention
The present invention relates to a substrate processing unit for performing various processings to a substrate, a method for detecting the position of a substrate, and a substrate processing apparatus.
2. Description of the Background Art
A substrate heating apparatus for heat-treating a substrate has been conventionally used in processing steps of a variety of substrates, such as a semiconductor wafer, glass substrate for a photomask, glass substrate for a liquid crystal display, and glass substrate for an optical disc (refer to JP 2001-189368 A, for example).
In the substrate heating apparatus, the substrate is placed on a heating plate for heat-treatment. During the heat-treatment, it is desired that the temperature of the entire substrate be varied uniformly. This improves accuracy of the processing steps.
For the purpose of improving accuracy of the processing steps, following solutions have been proposed.
For example, by providing a lid that covers the substrate above the heating plate, the substrate to be processed is prevented from being exposed to an airflow coming from above the substrate heating apparatus (downflow). The temperature of the entire substrate during the heat-treatment is therefore not affected by the downflow.
Moreover, when atmosphere during the heat-treatment is reduced, the substrate is prevented from being in contact with an unnecessary gas and reacting.
In addition to such solutions, it is required that the substrate be accurately placed during the heat-treatment. If the substrate is placed in a shifted position on the heating plate, part of the substrate lies out of the heating plate. As a result, the entire substrate may not be uniformly heat-treated.
By the way, a method for directly detecting the position of the substrate using an optoelectronic sensor, proximity sensor or the like has been conventionally used for knowing how the substrate is being transported or placed. This has led to attempts to obtain some information about the position of the substrate on the heating plate using an optoelectronic sensor, proximity sensor or the like.
It has been difficult however, in the above described heat-treatment apparatus, to install an optoelectronic sensor or proximity sensor to know the substrate position, because of the influence of heat from the heating plate or constraints and interference associated with the layout of other peripheral units in the substrate heating apparatus.
Apart from the optoelectronic sensor or proximity sensor, sensors such as a high heat-resistant optoelectronic sensor, weight measuring sensor for measuring the mass of the substrate, and temperature measuring sensor for detecting a temperature variation in the substrate heating apparatus are available; however, applying any of these to detect the substrate position in the substrate heating apparatus has been difficult because of problems associated with the space, cost necessary to install a plurality of sensors, sensor accuracy and the like.
For this reason, in a conventional substrate heating apparatus, positioning guides with a tapered portion are provided around the position in which the substrate is to be placed on a heating plate so as to prevent the substrate position from being shifted. In this case, even if the substrate is received in a shifted position, a peripheral edge of the substrate is guided by the tapered portion of a positioning guide, so that the substrate can be guided to a given position on the heating plate.
Thus, in the substrate heating apparatus, the substrate is heat-treated on the premise that it is placed in an accurate position by the positioning guides.
However, in the substrate heating apparatus with the positioning guides around the position in which the substrate is to be placed on the heating plate, the substrate may lie on a positioning guide when it is greatly shifted beyond a given range (such that the periphery thereof may lie beyond the tapered portion). In this case, the substrate is not guided to the given position on the heating plate, and heat-treated while being in a shifted position. As a result, the entire substrate is not uniformly heat-treated.